Moderately dispersed nano dy2o3

ABSTRACT

Dy 2 O 3  particles of a nanoparticle scale have beneficial properties for ceramic and electronic uses. Disclosed herein are moderately dispersed Dy 2 O 3  particles having regular morphology and lateral size ranging from about 10 nm to 1 μm. The Dy 2 O 3  particles may exhibit a narrow particle size distribution such that the difference between D 10  and D 90  is about 0.1 μm to 1 μm. Further disclosed are processes of producing these moderately dispersed Dy 2 O 3  particles. These processes do not include grinding to obtain the particles. Also disclosed herein are uses for these Dy 2 O 3 μ particles.

This application relates to moderately dispersed Dy₂O₃ particles having regular morphology and desirably small lateral sizes. These lateral sizes may range from about 10 nm to 1 μm. Also disclosed herein are processes of producing the moderately dispersed Dy₂O₃ particles and uses for same.

INTRODUCTION

Dysprosium Oxide (Dy₂O₃) is a sesquioxide compound of the rare earth metal dysprosium. It has specialized uses in ceramics, glass, phosphors, lasers, and in multilayer ceramic capacitors. In particular, it has uses as a photoluminescent and thermoluminescent material, in magnetic resonance imaging as a contrast agent, as well as an additive to the dielectric barium titanate component of multilayer ceramic capacitors to improve the electrostatic capacity.

In these uses, there is a need for small particle size dysprosium oxide achieved without grinding. Particle sizes for dysprosium oxide are generally approximately 7-8 microns.

Increasing efforts have been devoted to the preparation of nano-Dy₂O₃ materials, whose size, shape, crystal structure and surface chemistry meet the requirements of such technological applications.

A challenging issue is achieving a high yield synthesis of nano-Dy₂O₃ with precise control over the morphology (size, shape, surface chemistry, particle size dispersion, etc.). U.S. Pat. No. 6,677,262 discloses syntheses of narrowly dispersed Dy₂O₃ at low concentrations of precursor (8-10 g/L) via a urea route. However, the resultant yield of product was low. To synthesize Dy₂O₃ at high yields, the precursor concentrations must be greatly increased. However, at such high concentrations, the intermediates undergo further growth via Ostwald ripening or oriented attachment growth. See S. Deng et al., “Reduced Graphene Oxide Conjugated Cu₂O Nanowire Mesocrystals for High-Performance NO₂ Gas Sensor”, J. Am. Chem. Soc., 2012, 134(10), pp. 4905-4917. As such, the synthesized Dy₂O₃ does not retain the desired discrete and well-dispersed particles. Utilizing known syntheses, one cannot linearly extrapolate the concentration to produce nanoparticles at high yield due to the effect on the thermodynamics of particle growth.

Therefore, developing a simple and efficient method to prepare dispersed Dy₂O₃ at high yields remains needed.

SUMMARY

As disclosed herein, the present compositions comprise moderately dispersed Dy₂O₃ particles having regular morphology and lateral size ranging from about 10 nm (0.01 μm) to 1000 μm. In certain embodiments, the present compositions comprise moderately dispersed Dy₂O₃ particles having regular morphology and lateral size ranging from about 10 nm to 1 μm. In some embodiments, dispersed Dy₂O₃ particles have lateral size ranging from about 40 nm (0.04 μm) to 100 μm. In some embodiments, dispersed Dy₂O₃ particles have lateral size ranging from about 40 nm (0.04 μm) to 1 μm. In other embodiments, dispersed Dy₂O₃ particles have lateral size ranging from about 100 nm (0.1 μm) to 1 μm.

In any of these embodiments relating to lateral sizes, the Dy₂O₃ particles can have a relatively narrow particle size distribution such that the particles have a particle size distribution wherein D₁₀ and D₉₀ is about 0.1 μm to 1 μm.

The present processes of producing moderately dispersed Dy₂O₃ particles comprise: (a) mixing a dysprosium salt, polymeric additive, and chelating agent in water to provide a dysprosium precursor solution; (b) heating the dysprosium precursor solution to form a precipitate; and (c) calcining the precipitate to provide moderately dispersed Dy₂O₃ particles. From these processes, the moderately dispersed Dy₂O₃ particles can be isolated.

In embodiments of the process, the chelating agent can be selected from the group consisting of diethanolamine, 2-amino-2-(hydroxymethyl)-1,3-propanediol, triethanolamine, ethylenediamine, 6-aminohexanoic acid, L-histidine, L-lysine, and mixtures thereof.

In embodiments of the process, the polymeric additives can be selected from the group consisting of Polyvinylpyrrolidone (PVP), Poly(vinyl alcohol) (PVA), Polyethylenimine (PEI), and mixtures thereof.

Also disclosed herein are Dy₂O₃ particles made by this process. The process may provide for large scale production of these Dy₂O₃ particles and these processes may also provide for high yields. Importantly the processes do not include any grinding step.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a flowchart of an embodiment of the process of producing moderately dispersed Dy₂O₃ particles.

FIG. 2A is a SEM of nano Dy₂O₃ made by a chloride precursor/hydrothermal process.

FIG. 2B is a graph of particle size distribution of nano Dy₂O₃ made by the chloride precursor/hydrothermal process.

FIG. 3A is a SEM of nano Dy₂O₃ made by a nitrate precursor/hydrothermal process. These particles were made using aminohexanoic acid as the chelating agent and polyvinylpyrrolidone (PVP) as the polymeric additive.

FIG. 3B is a graph of particle size distribution of nano Dy₂O₃ made by a nitrate precursor/hydrothermal process and the chelating agent and polymeric additive as described for FIG. 3A.

FIG. 4A is a SEM of Dy₂O₃ synthesized using a nitrate precursor which involved precipitation at room temperature followed by a supercritical drying process, as described in Comparative Example 1.

FIG. 4B is a graph of particle size distribution of Dy₂O₃ as described for FIG. 4A and in Comparative Example 1.

FIG. 5A is a SEM of Dy₂O₃ synthesized using nitrate precursor which involved precipitation at room temperature followed by heating in isopropanol, as described in Comparative Example 2.

FIG. 5B is a graph of particle size distribution of Dy₂O₃ as described for FIG. 3E and in Comparative Example 2.

FIG. 6A is a SEM of Dy₂O₃ synthesized using nitrate precursor which involved precipitation at room temperature in the presence of carboxylic acid, as described in Comparative Example 3.

FIG. 6B is a graph of particle size distribution of Dy₂O₃, as described for FIG. 3G and in Comparative Example 3.

FIG. 7A is a Transmission Electron Micrograph (TEM) and selected area electron diffraction (SAED) pattern image of the dried precipitate using polyethylenimine (PEI) as the polymeric additive after hydrothermally reacting and drying.

FIG. 7B is a TEM and SAED of Dy₂O₃ using polyethylenimine as the polymeric additive after calcined.

FIG. 8A is a TEM and SAED image of dried precipitate using polyvinylalcohol (PVA) as the polymeric additive after hydrothermally reacting and drying.

FIG. 8B is a TEM and SAED of Dy₂O₃ using PVA as the polymeric additive after calcined.

FIG. 9 is an x-ray diffractogram of calcined Dy₂O_(3.)

FIG. 10 is an illustration of lateral size.

DETAILED DESCRIPTION

Before the moderately dispersed Dy₂O₃ particles and processes are disclosed and described, it is to be understood that this disclosure is not limited to the particular structures, process steps, or materials disclosed herein, but is extended to equivalents thereof as would be recognized by those ordinarily skilled in the relevant arts. It should also be understood that terminology employed herein is used for the purpose of describing particular embodiments only and is not intended to be limiting. It must be noted that, as used in this specification, the singular forms “a”, “an”, and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to “a step” may include multiple steps, reference to “producing” or “products” of a reaction or treatment should not be taken to be all of the products of a reaction/treatment, and reference to “treating” may include reference to one or more of such treatment steps. As such, the step of treating can include multiple or repeated treatment of similar materials/streams to produce identified treatment products.

Numerical values with “about” include typical experimental variances. As used herein, the term “about” means within a statistically meaningful range of a value, such as a stated particle size, concentration range, time frame, molecular weight, temperature, or pH. Such a range can be within an order of magnitude, typically within 10%, and even more typically within 5% of the indicated value or range. Sometimes, such a range can be within the experimental error typical of standard methods used for the measurement and/or determination of a given value or range. The allowable variation encompassed by the term “about” will depend upon the particular system under study, and can be readily appreciated by one of ordinary skill in the art. Whenever a range is recited within this application, every whole number integer within the range is also contemplated as an embodiment of the invention.

The present application relates to moderately dispersed Dy₂O₃ particles. Herein, dispersity is a measure of the heterogeneity (or uniformity) of particle sizes in a mixture. It can be indicated by the polydispersity index (PDI) parameter as derived from the dynamic light scattering (DLS) technique, which is commonly used to determine the size distribution of particles in suspension by measuring the fluctuations in intensity of the scattered light. Specifically, from the particle size distribution (PSD) profile, the mean and standard deviation (stddev) are obtained and expressed in the form of (stddev/mean)² to yield the PDI value. Information on this analysis technique also can be found at https://www.materials-talks.com/blog/2017/10/23/polydispersity-what-does-it-mean-for-dls-and-chromatography/, which is herein incorporated by reference as needed.

TABLE 1 Approximate values for dispersity parameters Distribution Type monodisperse polydisperse Definition uniform narrow moderate broad PDI from =(stddev/mean)² 0.0 0.0-0.1 0.1-0.4 >0.4 DLS As illustrated in Table 1, the PDI value for a perfectly uniform sample is 0.0. As used herein, “moderately dispersed” means that the PDI value of Dy₂O₃ particles is in the range of about 0.1 to 0.4.

As used herein, “moderately dispersed Dy₂O₃ particles” means Dy₂O₃ particles having a particle size distribution wherein D₁₀ to D₉₀ is not more than about 1 μm. In some embodiments, the particles have a particle size distribution wherein D₁₀ and D₉₀ is about 0.1 μm to 1 μm.

As used herein, “regular morphology” means that the characteristics of particles, including their size, shape and structure, are clearly defined and common across different particles in the same batch. It includes small aspect ratio configurations, such as uniform spheres, ovals or cubes, as well as high aspect ratio configurations such as uniform rods or wires.

As used herein, in two-dimensional nanostructures “lateral size” refers to the length extending from one side to the other side. FIG. 10 provides an illustration of lateral size and how it is measured. Herein, the lateral size of particles can be measured from electron microscopy images, specifically the transmission electron and scanning electron microscopy (TEM and SEM) images.

Disclosed herein is a composition comprising moderately dispersed Dy₂O₃ particles having regular morphology and lateral size ranging from about 10 nm (0.01 μm) to 1000 μm. In certain embodiments, the present compositions comprise moderately dispersed Dy₂O₃ particles having regular morphology and lateral size ranging from about 10 nm to 1 μm. In some embodiments, dispersed Dy₂O₃ particles have lateral size ranging from about 40 nm (0.04 μm) to 100 μm. In some embodiments, dispersed Dy₂O₃ particles have lateral size ranging from about 40 nm (0.04 μm) to 1 μm. In other embodiments, dispersed Dy₂O₃ particles have lateral size ranging from about 100 nm (0.1 μm) to 1 μm. In these embodiments of lateral size, the particles have a particle size distribution wherein D₁₀ and D₉₀ is about 0.1 μm to 1 μm.

In all of the above set forth embodiments relating to particle size distribution and lateral size, the Dy₂O₃ particles can have a D₁₀ of about 10 nm to 100 nm, a D₅₀ of about 0.1 μm to about 0.8 μm, and a D₉₀ of about 0.25 μm to 10 μm. In some embodiments, the Dy₂O₃ particles can have a D₁₀ of about 10 nm to 100 nm, a D₅₀ of about 0.1 μm to about 0.8 μm, and a D₉₀ of about 0.25 μm to 5 μm. In certain of these embodiments, the Dy₂O₃ particles can have a D₉₀ of about 0.25 μm to 1 μm.

In particular embodiments, the Dy₂O₃ particles have a D₅₀ of about 10 nm to 0.2 μm and a D₉₀ of about 0.2 μm to about 1 μm. In certain of these embodiments, the Dy₂O₃ particles have a D₅₀ of about 10 nm to 0.15 μm and a D₉₀ of about 0.2 μm to 0.75 μm.

The Dy₂O₃ particles disclosed herein can have a round or faceted shape, and do not agglomerate in any significant way. In addition, the Dy₂O₃ particles disclosed herein have a crystalline structure. In certain embodiments, the X-ray diffraction pattern of the Dy₂O₃ particles illustrates a single cubic phase, which can serve as a fingerprint for the periodic atomic arrangements in the material.

In any of the embodiments set forth above, the Dy₂O₃ particles also can have a low chloride content and in certain of these embodiments the chloride content can be about 0 to 50 ppm. Such low chloride content would prevent or reduce the likelihood of corrosion and is especially important for applications of the Dy₂O₃ particles in multilayer ceramic capacitors. Thus, achieving the low chloride content is an important characteristic of the Dy₂O₃ particles.

The moderately dispersed Dy₂O₃ particles as disclosed herein are made by a process comprising: (a) mixing a dysprosium salt, polymeric additive, and chelating agent in water to provide a dysprosium precursor solution; (b) heating the dysprosium precursor solution to form a precipitate; and (c) calcining the precipitate to provide moderately dispersed Dy₂O₃ particles. From this process, the moderately dispersed Dy₂O₃ particles as disclosed herein can be isolated.

It is important to note that the processes disclosed herein do not include a grinding or milling step. As such, the disclosed Dy₂O₃ particles are obtained without any grinding or milling step. Accordingly, the disclosed process provides the Dy₂O₃ particles as disclosed and described above.

The starting dysprosium salt is water soluble and in the process, the dysprosium salt is dissolved in water. The salts can be salts of inorganic or organic acids, for example chloride, sulfate, nitrate, acetate, and the like. In certain embodiments, the dysprosium salt can be either a chloride or nitrate salt. The starting dysprosium salt can affect the particle shape, particle size, and particle size distribution achieved.

The chelating agent used in the processes described herein can be any chelating agent. The chelating agents are organic compounds capable of linking metal ions to form chelates. In certain embodiments, the chelating agent can be advantageously selected from among diamines (e.g. ethylenediamine), alkanolamines (e.g. diethanolamine, 2-amino-2-(hydroxymethyl)-1,3-propanediol and triethanolamine) or amino acids (e.g. 6-aminohexanoic acid, L-histidine, L-lysine), and mixtures thereof. One or more chelating agents can also be present in the same reaction mixture. During calcination, the chelating agent is removed.

The polymeric additive can be any polymer that assists in processability of the dysprosium precursor solution and is removed during calcination. Herein, the role of the polymeric additive is to affect the particle size and morphology by providing selective surface stabilization and/or access to kinetically controlled growth conditions. The polymeric additive can be selected from the group consisting of Polyvinylpyrrolidone (PVP), Poly(vinyl alcohol) (PVA), Polyethyleneimine (PEI), and mixtures thereof.

The chelating agent and polymeric additive are dissolved in water when added to the process. The chelating agent may be added as a water mixture that is approximately 0.1 to 2 M, and in some embodiments about 0.5 to 1 M. The polymeric additive may be added as a water mixture that is approximately 2 to 15 g/L, and in some embodiments about 6.25 to 12.5 g/L.

For the addition to create the dysprosium precursor solution, the water mixtures of chelating agent, polymeric additive, and dysprosium salt can be added simultaneously or individually with mixing. Any order of addition can be utilized, if not added simultaneously. In some embodiments, about 2 to 3 moles of chelating agent are added per mole of dysprosium in step (a) of the process.

In certain embodiments, the dysprosium precursor solution of step (a) has a dysprosium concentration of about 0.2 mol/L to 1.5 mol/L.

The dysprosium precursor solution of step (a) can have a dysprosium oxide concentration of about 25 to 75 g/L.

The dysprosium precursor solution is heated in step (b) to form a precipitate. The heating can be conducted at a temperature of about 100° C. to 350° C. and for from about 15 mins to 24 hours. In certain embodiments, the heating can be conducted at a temperature of about 120° C. to 160° C. and for from about 45 min to 2 hours. The heating provides a crystalline precipitate. In particular, the heating can provide a single crystalline precipitate.

The crystalline precipitate from the heating process of step (b) can be washed with water to remove residual quantities of bound or adsorbed ions, such as nitrates and chlorides, and then dewatered with an appropriate solvent, such as ethanol, before calcining. In certain embodiments, the crystalline precipitate is particularly pure in anionic impurities, as characterized by a conductivity of less than about 10 mS/cm after washing.

The crystalline precipitate is calcined in step (c) to result in Dy₂O₃ particles as disclosed and described herein. The calcining can be conducted at a temperature ranging from about 400° C. to 1000° C. and for from about 15 mins to 24 hours. The calcining should be sufficient to remove the polymeric additive and the chelating agent. In certain embodiments the calcining can be conducted at a temperature of from about 600° C. to 800° C. and for from about 1 to 4 hours.

The calcining results in the Dy₂O₃ particles with the properties as set forth herein. Similar to the precipitate of step (b), the calcined products can exhibit a single crystalline SAED (selected area (electron) diffraction).

Calcining can be conducted in any way that results in a uniform material.

For Particle Size Dispersion measurements (PSD) as referenced herein, about 0.1 g of powder was dispersed in 10 mL of 2% Sodium Hexametaphosphate by sonication for 3 minutes. The PSD measurement was then conducted with Microtrac S3500. The sample solution was dropped into the sample delivery controller filled with DI water followed by 3 minute sonication. The solution was then flowed through a transparent cell at a flow rate of 49 mL/sec (75% flow rate). Signals are captured and sample particle size was calculated by the machine.

FIG. 1 is a flow chart for an embodiment of a process of producing moderately dispersed Dy₂O₃ particles.

FIGS. 2 and 3 shows typical morphology of claimed Dy₂O₃ by A) SEM or B) Microtrac.

In the following, Examples are given to illustrate the inventive method for the preparation of Dy₂O₃ particles and characterization thereof in more detail, although the scope of the invention is never limited thereby in any way.

EXAMPLES Example 1: Synthesis of Nano-Dy₂O₃

The following was done:

1) The polymeric additive PVA and chelating agent diethanolamine are weighed and subsequently dissolved in water with heating at 50° C.

2) A stock solution of DyCl₃ (415 g/L, 2.225 M) was added to the above mixture to a final concentration of 0.4 M (74.6 g/L).

3) The solution is poured into an autoclave teflon liner and the autoclave was heated to 160° C. and held at this temperature for 1 hour.

4) The result was a viscous white material (wetcake/precipitate).

5) The wetcake was then centrifuged and the supernatant removed. Subsequently, the wetcake was washed with deionized water to a conductivity of less than 8 mS/cm.

6) The wetcake was dewatered by washing with ethanol two times.

7) The wetcake was calcined at 700° C. for 2 hours.

As examined with a scanning electron microscope, the dysprosium oxide comprised discrete non-agglomerated particles with round and faceted morphology (FIG. 2A). PSD of the Dy₂O₃ shows particles with a D₅₀ value of 0.13 μm (FIG. 2B). TEM and SAED of the Dy₂O₃ showed the material to possess a single crystalline structure.

Example 2: Synthesis of Nano-Dy₂O₃

The following was done:

1) 8 g/L PVP (MW=40K) and PVP (MW=1300K), 0.06M of aminohexanoic acid and 0.8M of DEA were dissolved in water.

2) A stock solution of Dy(NO₃)₂ (415 g/L, 2.225 M) was added to the above mixture to a final concentration of 0.4 M (74.6 g/L).

3) The solution was then poured into an autoclave teflon liner and heated to 160° C. and kept at this temperature for 1 hour.

4) The result was a viscous white material (wetcake/precipitate).

5) The wetcake was centrifuged, and the supernatant removed. The remaining material was washed with deionized water to a conductivity of less than 8 mS/cm.

6) The wetcake was then dewatered by washing with ethanol two times and centrifuged to obtain the final wetcake.

7) The wetcake was calcined at 700° C. for 2 hours.

SEM of the resultant dysprosium oxide showed that it comprised discrete non-agglomerated particles with flat morphology and length of less than 500 nm (FIG. 3A). PSD of the resultant Dy₂O₃ showed that the particles had a D₅₀ of 0.137 μm (FIG. 3B).

Comparative Example 3: Synthesis of Dy₂O₃

The following was done:

1) 1083 ml of 4.5M NH₄OH was prepared.

2) A stock solution of 900 ml of Dy(NO₃)₃ (100 g/L, 2.225 M) was prepared and added to the above ammonia solution to a final concentration of 0.4 M (74.6 g/L).

3) The solution was stirred at room temperature for 1 hour.

4) The final pH was 9.90 and the temperature was 24.1° C.

5) The precipitates were collected by decanting the supernatant and replenishing with deionized water several times until the conductivity of filtrate is less than 8 mS/cm.

6) Two-thirds of the precipitates obtained from step 5 were dewatered with ethanol and dispersed in a total volume of 600 ml ethanol.

7) The slurry was subjected to drying at 300° C. and 130-140 bar.

8) The resultant oxide was calcined at 700° C. for 2 hours.

The resultant Dy₂O₃ consisted of agglomerated fine needle-like particles (FIG. 4A). PSD of the material showed that it was comprised of particles with a D₅₀ of 3.181.1 m (FIG. 4B).

Comparative Example 4: Synthesis of Dy₂O₃

The following was done:

1) Steps 1-5 of Comparative Example 1 were followed.

6) One-third of the precipitates obtained were dewatered with isopropanol and dispersed in a total volume of 500 ml isopropanol.

7) The slurry was heated to 80° C. for 24 hours.

8) The resultant wetcake was calcined at 700° C. for 2 hours.

The resultant Dy₂O₃ consisted of large irregular agglomerates of chunks and clusters (FIG. 5A). PSD of these agglomerates showed that they had a D₅₀ of 7.08 μm (FIG. 5B).

Comparative Example 5: Synthesis of Dy₂O₃

The following was done:

1) 120 ml of 4.5M NH₄OH was prepared; 5 g of Lauric acid was dissolved in this ammonia solution.

2) A stock solution of 100 ml of Dy(NO₃)₃ (100 g/L, 2.225 M) was prepared and added to the above mixture.

3) The solution is stirred at room temperature for 1 hour.

4) The final pH was 9.73 and the temperature was 21.8° C.

5) The precipitates were collected by decanting the supernatant and replenishing with deionized water several times until the conductivity of filtrate is less than 8 mS/cm.

8) The wetcake was collected by suction filtration using a Buchner funnel.

9) The resultant wetcake was calcined at 700° C. for 2 hours.

Clusters of agglomerates of various sizes of Dy₂O₃ resulted (FIG. 6A). PSD showed they had a D₅₀ of 21.54 μm (FIG. 6B).

Example 6—Forming a Multi-Layer Ceramic Capacitor Using Moderately Dispersed Dy₂O₃ Particles

-   -   1. Mix the moderately dispersed Dy₂O₃ particles as prepared         herein with barium titanate powder (main ingredient) and other         raw material powders (e.g. MgO, Y₂O₃, V₂O₅, Ho₂O₃).     -   2. Subject the powder mixture to wet mixing in a mixed solvent         system of polyvinyl butyral (PVB) resin solution, toluene and         ethanol to form a ceramic slurry. Next, cast the slurry into         ceramic green sheets using the doctor blade method.     -   3. Imprint the ceramic green sheets with an internal electrode         pattern, then laminate on each of the upper and lower sheet         surfaces.     -   4. Compact the ceramic green sheets together using a pressing         machine, then cut the resultant sheet laminate into a specific         size.     -   5. Fire the sheet laminate for 2 hours at 1120 to 1135° C. to         form the capacitor main body, then apply an external electrode         paste containing Cu powder and glass to both ends of the fired         capacitor main body and print at 850° C. to form the external         electrode.     -   6. Employ an electrolytic barrel machine to plate Ni and Sn         successively, thereby producing a multi-layer ceramic capacitor.

Unless otherwise indicated, all numbers expressing quantities of ingredients, properties such as molecular weight, reaction conditions, and so forth used in the specification and claims are to be understood as being modified in all instances by the term “about.” Accordingly, unless indicated to the contrary, the numerical parameters set forth in the following specification and attached claims are approximations that may vary depending upon the desired properties sought to be obtained.

Notwithstanding that the numerical ranges and parameters setting forth the broad scope of the technology are approximations, the numerical values set forth in the specific examples are reported as precisely as possible. Any numerical value, however, inherently contain certain errors necessarily resulting from the standard deviation found in their respective testing measurements.

It will be clear that the compositions and methods described herein are well adapted to attain the ends and advantages mentioned as well as those inherent therein. Those skilled in the art will recognize that the methods and systems within this specification may be implemented in many manners and as such are not to be limited by the foregoing exemplified embodiments and examples. In this regard, any number of the features of the different embodiments described herein may be combined into one single embodiment and alternate embodiments having fewer than or more than all of the features herein described are possible.

While various embodiments have been described for purposes of this disclosure, various changes and modifications may be made which are well within the scope contemplated by the present disclosure. Numerous other changes may be made which will readily suggest themselves to those skilled in the art and which are encompassed in the spirit of the disclosure. 

1. A composition comprising moderately dispersed Dy₂O₃ particles having regular morphology and lateral size ranging from about 10 nm to 1 μm.
 2. The composition of claim 1, wherein the lateral size ranges from about 40 nm to 1 μm.
 3. The composition of claim 1, wherein the lateral size ranges from about 100 nm to 1 μm.
 4. The composition of claim 1, wherein the particles have a particle size distribution wherein D₁₀ and D₉₀ is about 0.1 μm to 1 μm.
 5. The composition of claim 1, wherein the particles have a D₁₀ of about 10 nm to 100 nm, a D₅₀ of about 0.1 μm to about 0.8 μm, and a D₉₀ of about 0.25 μm to 10 μm.
 6. The composition of claim 5, wherein the particles have a D₉₀ of about 0.25 μm to 5 μm.
 7. The composition of claim 5, wherein the particles have a D₉₀ of about 0.25 μm to 1 μm.
 8. The composition of claim 1, wherein the particles are spheres, ovals, or cubes.
 9. The composition of claim 1 comprising about 0 to 50 ppm chloride.
 10. The composition of claim 1, wherein the particles have a single cubic phase.
 11. A process of producing moderately dispersed Dy₂O₃ particles comprising: (a) mixing a dysprosium salt, polymeric additive, and chelating agent in water to provide a dysprosium precursor solution; (b) heating the dysprosium precursor solution to form a precipitate; and (c) calcining the precipitate to provide moderately dispersed Dy₂O₃ particles.
 12. The process of claim 11, wherein the chelating agent is selected from the group consisting of diethanolamine, 2-amino-2-(hydroxymethyl)-1,3-propanediol, triethanolamine, ethylenediamine, 6-aminohexanoic acid, L-histidine, L-lysine, and mixtures thereof.
 13. The process of claim 11, wherein the polymeric additives is selected from the group consisting of Polyvinylpyrrolidone (PVP), Poly(vinyl alcohol) (PVA), Polyethylenimine (PEI), and mixtures thereof.
 14. The process of claim 11, wherein the dysprosium salt is a water-soluble salt.
 15. The process of claim 14, wherein the water-soluble salt of dysprosium is a chloride or nitrate salt.
 16. The process of claim 11, wherein the dysprosium precursor solution of step (a) has a dysprosium concentration of about 0.2 mol/L to 1.5 mol/L.
 17. The process of claim 11, wherein the dysprosium precursor solution of step (a) has a dysprosium oxide concentration of about 25 to 75 g/L.
 18. The process of claim 11, wherein about 2 to 3 moles of chelating agent are mixed per mole of dysprosium in step (a).
 19. The process of claim 11, wherein the heating is conducted at a temperature ranging from about 100° C. to 350° C. and for from about 15 mins to 24 hours.
 20. The process of claim 11, wherein the heating of (b) provides a single crystalline precipitate before calcining.
 21. The process of claim 11, wherein the calcining is conducted at a temperature ranging from about 400° C. to 1000° C. and for from about 15 mins to 24 hours.
 22. The process of claim 11, wherein the calcining provides moderately dispersed Dy₂O₃ particles having regular morphology and lateral size ranging from about 40 nm to 1 μm.
 23. The process of claim 11, wherein the process does not include grinding.
 24. (canceled) 